PROLOG This manual page is part of the POSIX Programmer
s Manual. The Linux implementation of this interface may
differ (consult the corresponding Linux manual page for
details of Linux behavior), or the interface may not be
implemented on Linux.

NAME fdim, fdimf, fdiml - compute positive difference
between two floating- point numbers

DESCRIPTION These functions shall determine the positive
difference between their arguments. If x is greater than y,
x- y is returned. If x is less than or equal to y, +0 is
returned.

An application wishing to check for error situations
should set errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions.
On return, if errno is non-zero or fetestexcept(FE_INVALID |
FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an
error has occurred.

If x- y is positive and overflows, a range error shall
occur and fdim(), fdimf(), and fdiml() shall return the
value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.

If x- y is positive and underflows, a range error may
occur, and either ( x- y) (if representable), or 0.0 (if
supported), or an implementa- tion-defined value shall be
returned.

If x or y is NaN, a NaN shall be returned.

ERRORS The fdim() function shall fail if:

Range Error The result overflows.

If the integer expression (math_errhandling &
MATH_ERRNO) is non-zero, then errno shall be set to
[ERANGE]. If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, then the overflow
floating-point exception shall be raised.

The fdim() function may fail if:

Range Error The result underflows.

If the integer expression (math_errhandling &
MATH_ERRNO) is non-zero, then errno shall be set to
[ERANGE]. If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, then the underflow
floating-point exception shall be raised.

The following sections are informative.

EXAMPLES None.

APPLICATION USAGE On implementations supporting IEEE Std
754-1985, x- y cannot underflow, and hence the 0.0 return
value is shaded as an extension for implemen- tations
supporting the XSI extension rather than an MX
extension.

On error, the expressions (math_errhandling &
MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are
independent of each other, but at least one of them must be
non-zero.

COPYRIGHT Portions of this text are reprinted and
reproduced in electronic form from IEEE Std 1003.1, 2003
Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the
Institute of Electrical and Electronics Engineers, Inc and
The Open Group. In the event of any discrepancy between this
version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .